1. Field of the Invention
The present invention relates to a slim, compact high, magnification zoom lens.
2. Description of the Related Art
A zoom lens system for a still camera or a video camera must usually be compact and have superior optical performance and a high magnification ratio. As electronic devices such as portable information terminals, personal digital assistants (PDAs), and mobile phones become more popular, they now often include a digital imaging unit or digital video unit. Accordingly, the demand for compact cameras is further increased. As digital cameras become popular, people wish to carry them constantly, regardless of the need for photography, unlike film cameras, and thus the demand for compact, slim, and lightweight cameras is increasing.
Slim, compact cameras are classified as a slider type in which the zoom lens protrudes out of the camera body during use and is kept inside the camera body when not used, and a refraction type in which a reflector such as a prism is used to reduce the thickness of a lens system.
The thickness of a refraction type optical system including a prism can be minimized by changing the optical path of light by 90° in the middle of the optical system using the prism. For slim, compact digital cameras, a 3× zoom is common but the demand for high magnification of over 5× zoom is increasing.
Japanese Patent Publication No. 2003-202500 discloses the zoom lens shown in FIG. 1, which consists of a first lens group Gr1 including a reflection surface which has a positive refractive power and changes the optical axis by 90°, a second lens group Gr2 having a negative refractive power, a third lens group Gr3 having a positive refractive power, a fourth lens group Gr4 having a positive refractive power, and a fifth lens group Gr5. All the lens groups are separated from each other by air gaps which vary when changing the magnification.
The magnification of the zoom lens optical system can be changed by a factor of about 3 to 6. The reflection member is relatively large and two or more lenses are arranged in front of the reflection member. As a result, the size of this optical system is undesirably large for a slim, compact camera.